The present invention relates to a variable-pitch arm star construction for rotary molding machines for making, by drawing and blowing, plastic vessels and bottles, and a rotary molding machine comprising the star construction.
More specifically, the field of the invention is that of the machines which are used for making plastic material bottles and vessels, particularly of PET, by a drawing-blowing molding process, carried out starting from a molded preform.
For making the above mentioned bottles or vessels, a starting preform or parison, consisting of a tubular PET body having a closed bottom, is heated to a desired molding temperature, drawn, pre-blown and blown to a final forming pressure, for forming the bottle inside the mold.
In the above mentioned types of molding machines, the molds are rotatably supported on a supporting star or wheel construction, upstream and downstream of which are provided star arrangements, respectively for supplying the parisons and removing the blown bottles.
In particular, the star construction designed for feeding the parisons to the mold must be adapted to receive the parisons from a rotary feeder having a small operating pitch, and to transfer the received parison toward the mold supporting wheel, which has a larger pitch.
Variable pitch arm star construction are also known: however, they are greatly complex, and their variable pitch can be replaced or re-timed only by performing very difficult operations.